Measurement of the transmittance, absorbance or other transmission characteristics of a liquid sample by an ultraviolet-visible spectrophotometer or other spectrophotometers generally uses a prism-like or cylindrical cuvette cell holding the liquid sample. However, in the fields of biochemistry in which the quantities of proteins or DNAs need to be determined, the cuvette cell cannot be used because in most cases the quantity of the liquid sample to be analyzed is extremely small.
An example of conventional apparatuses for spectrometric measurement of a trace liquid sample is the ND-1000 Spectrophotometer sold by NanoDrop Technologies, LLC (http://www.nanodrop.com/nd-1000-overview.html, “NanoDrop ND-1000 Overview”, NanoDrop Technologies, LLC, Jul. 24, 2007). As shown in FIG. 13, this apparatus (called the “first conventional apparatus” hereinafter) has upper and lower bases 80 and 82 vertically facing each other with a predetermined gap, across which a liquid sample 84 can be held in a vertically expanded form by surface tension. In this state, a light-projecting optical fiber 81 inside the upper base 80 delivers a measurement light into the liquid sample 84. The light transmitted through the sample is received by a light-receiving optical fiber 83 inside the lower base 82. The received light is used to perform a spectrometric analysis or other measurements.
Another conventional example is the “optical measurement instrument for trace liquid sample” disclosed in PCT/JP06/307032 (WO 2007/113895), which is an international patent application filed by Shimadzu Corporation. As shown in FIG. 14, this instrument (called the “second conventional apparatus” hereinafter) includes a disk-shaped rotary sample plate 91 with a plurality of sample-holding portions 92 in the vicinity of its circumference. In a measurement by this apparatus, a liquid sample is initially dropped onto the sample-holding portion 92 at a sample supply position U1. Subsequently, the sample plate 91 is turned until the sample-holding portion 92 reaches a measuring position U2. Then, a transparent window plate 22 is lowered from above to create an optical path of a specific length. In this state, the transmitted light is measured. After the measurement is completed, the window plate 22 is raised, and the sample plate 91 is turned so that the sample-holding portion 92 is moved from the measuring position U2 to a wiping position U3, where the sample liquid is removed by a liquid-absorptive cleaning pad 93. Meanwhile, with the window plate 22 in the raised position, the liquid sample remaining on the lower surface of the window plate 22 is wiped off by a wipe material (which is not shown) separate from the cleaning pad 93.
The first conventional apparatus requires cleaning the end faces of both the light-projecting and light-receiving optical fibers, using a wipe material such as a waste paper, after the measurement of one sample is completed and before the measurement of the next sample is initiated. This cleaning task consumes a considerable amount of time since it is a manual operation to be performed every time the measurement of one sample is completed.
The second conventional apparatus requires complicated mechanisms consisting of a large number of parts for turning the sample plate 91 and cleaning the sample-holding section 92 and window plate 22 with the separate wipe materials.
Another problem of the second conventional apparatus is that the semi-automated sample-wiping mechanism requires the wipe materials to be manually exchanged. Although this job does not need to be performed for every completion of the measurement, the process is rather complicated and consumes considerable time and labor.
The present invention has been developed in view of these problems, and its first objective is to provide a wiping mechanism for quickly and efficiently wiping off a liquid sample in an optical measurement apparatus for a trace liquid sample.
The second objective of the present invention is to provide a wipe-material holding mechanism enabling the wipe material for wiping off a liquid sample to be quickly and easily exchanged in a wiping mechanism for an optical measurement apparatus.